This invention relates generally to a dot printer of the type used in miniaturized printers, and more particularly, to a printer suited to a matrix type output. In recent years, electric calculators have been made in remarkably small sizes as a result of improvement in mounting technology. In particular, great contributions have been made through increased density and the reduction of power consumption through large scale integration (LSI) of circuits, thinning and reduction in power consumption of the liquid crystal display means which are generally used, and simplifications in the keyboard.
With regard to an electric calculator equipped with a printer, suitable progress in miniaturization and power consumption reduction of the printer makes it possible to produce a convenient electric calculator with printer which is entirely portable when driven by means of an internal battery. However, because printing is accomplished by means of a print character ring of a printing character drum provided with raised characters on the outer peripheries, it is not possible to print more than the characters and signs that are already present on the rings or drums. Accordingly use of the printer is extremely limited. Therefore, a dot printer of ultra-small size and having a lower power consumption, which can print characters, signs and graphics very freely by means of a dot matrix, is desirable. Presently, various types of dot printers are in use or proposed. However, most of these dot printers are complicated in construction and large in size. Further, they require a high voltage for driving and consume substantial quantities of electrical power. Thus, they are not suitable for a convenient hand held or portable electric calculator with printer.
For example, in a conventional wire dot printer, which prints by means of a plurality of wires, an electromagnet having a hinge action or a plunger action is used as a driving power source which reciprocates the wires. In a printer using a plunger-type electromagnet, a wire is directly fixed on a plunger. The plunger is drawn into a hollow portion of the coil so that the attached wire goes in and out with the plunger. In this design, the gap between the platen for printing and the tip of the wire is no more or less than the stroke of the plunger. Because inadvertent contact between the ribbon and paper must be avoided, the stroke must be long and the gap between the plunger is large. The attractive force of the electromagnet is provided only with high inputs of electrical energy. Accordingly, electrical efficiency of the electromagnet is extremely poor and high voltage and high current are necessary for driving the wire in a short period of time measured in microseconds.
On the other hand, in a printer using a hinged-type electromagnet, the wire is extended out from a hinge beyond the electromagnet. Then it is possible to make the gap in the electromagnet smaller than the gap between the platen and the end of the wire. But the drawing power of the electromagnet in a printer of this type is less than the drawing power in a printer using a plunger-type electromagnet where the plunger is drawn into a hollow portion of the coil. Again, efficiency of the electromagnet is extremely poor and high voltage and high current are again necessary for a printer using a hinge-type electromagnet construction. Both of these printers are constructed where the impacting ends of a plurality of wires are arranged in a row. As a result, the structure is complicated and large as well as inefficient.
Controlling the stroke of the wire, that is, the gap in the electromagnet, by means of screws and the like, or not controlling the gap at all, presents difficulties. In the first instance, the cost of production is raised, and in the second instance, a large current is necessary for driving because suitable printing must be assured regardless of the variations in the gap. Also, it should be understood that when simultaneously driving a plurality of wires, the peak current drain is very large and the use of batteries is disadvantageous either through incapacity to deliver sufficient current or short operating life.
What is needed is a dot printer which is small in size, simple in construction, reliable, and uses low electrical energy while producing high quality printing.